The 30-year-old driver, from Five Ashes in East Sussex, has set his sights on winning the series after a triumphant start to the season.
Sumpter, who was competing in the Pirelli Porsche Cup last year, has moved into the Privilege Insurance British GT Championship and, together with co-driver Mike Jordan, they won the opening round at Thruxton.
Against the might of former British Touring Car champion John Cleland and Formula 3 ace Warren Hughes, Sumpter and Jordan blasted their Porsche 911 GT3R to victory in the GTO category.
Sumpter said: "I have been doing the Porsche Cup for five years and I wanted to move on to something more powerful.
"The GTs are more powerful cars and the time was right for change. This is a new challenge for me.
"It is nice to mix it with Vipers, TVRs and Ferraris. In this series you are running against other sports cars."
The GT series is different to the Porsche Cup, most notably because there are two drivers for each car.
Sumpter explained: "Each race is an hour long. In between 25 and 35 minutes you go into the pits, swap drivers and get out as quick as you can.
"It is endurance racing and it is a team effort, which I like. The pit crew, the second driver and everybody else plays their part.
"I like the excitement of team endurance racing."
Sumpter could not have expected a better start to the season, especially as his Porsche 911 GT3R, one of four such cars in the race, had only arrived a week before.
At a high speed Thruxton circuit, with changeable weather, the Paragon-Porsche entered car qualified first in the GTO category.
In the race itself, Sumpter drove a superb opening stint to keep well in touch with Cleland before handing over the car to Jordan at half distance.
Jordan was quickly into his stride and set about chasing Hughes. Within a couple of laps the cars were nose to tail and, after some great wheel-to-wheel dicing, Jordan edged ahead on lap 20.
Once in front, Jordan was not about to surrender his lead, although Hughes kept the pressure on all the way to the flag and was only a second and a half behind after 60 minutes of flat out racing.
Sumpter said: "We had only got the car a week before, so it was a dream start for us.
"I always start every season hoping to win the championship and this year is no different.
"After winning the first round, we are starting to think it is not that far fetched to win it this year."
The second of the 12 round series is at Croft in North Yorkshire this weekend. The Thruxton race will be screened on Channel 4 at 11am next Saturday.
l RACING for the Sussex-based garage Paragon Porsche, owned by Mark Sumpter, John Williams finished second in the opening round of the Pirelli Porsche Classic Championship at Snetterton.
Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.
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